This invention relates to heat exchange catheters, and particularly to catheters that exchange heat with the blood stream of a patient.
Heat exchange catheters are used in many instances for a variety of reasons. Some surgeries, for example, are better performed when the patient cools to a hypothermic state. In other instances, a patient may suffer from accidental hypothermia and may need to be warmed to a normothermic temperature e.g. 98.6xc2x0 F. Some heat exchange catheters include the capability of infusing fluids such as nutrition, medicine and contrast agents into the blood.
Post surgical patients risk infection and fever. A fever can be controlled through the use of a heat exchange system having an intravascular heat exchange catheter. One such system is disclosed in U.S. Pat. No. 6,146,411. This U.S. Patent is incorporated herein by reference and teaches an exemplary system used to achieve patient normothermia.
The principals of heat exchange applicable to any flowing medium (including blood) dictates the amount of heat transfer. In blood, the heat transferred depends on many things including the volumetric flow rate of the blood, the geometry of the heat exchanger and the temperature difference between the heat exchanger and the blood.
Various heat exchange catheter designs have been developed. U.S. Pat. No. 6,126,684, for example, teaches a heat exchange catheter having tubular balloons in serial alignment to exchange heat with the blood stream of a patient. This U.S. Patent is incorporated herein by reference. The balloons allow for a relatively large surface area of contact for heat exchange. Infusion lumen exit ports are defined between the balloons. Unfortunately, these exit port regions limit the effective heat exchange surface area.
Heat exchange catheter balloons can be sized having an external volume that optimally exchanges heat with the flowing blood. The balloon internal volume, however, is large enough to inhibit optimal mixing of the heat exchange fluid. Boundary layers of heat exchange fluid can form in the interior of such balloons, lowering the temperature gradient between the heat exchange fluid at the balloon internal surface and ultimately reducing the effective rate of heat transfer between the heat transfer fluid and the flowing blood.
Heat exchange catheters have been developed that deliver the heat exchange fluid to the distal end of the catheter via an insulated delivery lumen, causing the heat exchange fluid to maintain a relatively uniform temperature until the heat exchange fluid returns via a return lumen to exchange heat with the flowing blood. This improves the temperature gradient between the heat exchange fluid within the interior balloon walls and the flowing blood, unfortunately, the residence time that the heat exchange fluid interacts with the flowing blood is limited.
Blood has a maximum desirable heating limit because above certain temperatures blood proteins can degenerate and coagulation may occurr. This limits the maximum operating temperature of known intravasculature catheters. Because the operating temperature of an intravascular catheter is limited, the catheter geometry takes on an increased importance to effectuate overall heat transfer.
What is desired is a heat exchange catheter having a geometry that is optimally designed for transferring heat to flowing blood.
A heat exchange catheter includes a catheter body having an inflow lumen, an outflow lumen, a proximal region and a distal region. A first balloon helically wraps around at least a portion of the catheter body and maintains fluid communication with the inflow lumen. A second balloon helically wraps around at least a portion of the catheter body and maintains in fluid communication with the outflow lumen. The first and second balloons forming a fluid circuit to facilitate circulation of a heat exchange fluid through the first balloon and the second balloon.
Optimally, the first and second balloons are inflatable from a flattened configuration where the balloons lie flush with the catheter body to an operational configuration where the heat exchange fluid inflates the balloons. The flattened configuration facilitates insertion of the catheter into the body of a patient. Preferably, the catheter inserts into the central vasculature.
The catheter body defines a core extending between the proximal region and the distal region. The inflow lumen and the outflow lumen being defined within the core in the proximal region. The balloons further define the inflow and outflow lumens in the distal region. The core also defines a guidewire lumen.
The first balloon and second balloon wrap around the distal region. According to one aspect of the invention, the balloons define a gap there between. According to an alternate aspect of the invention, the balloons tightly wrap and forms a gap only to expose an exit port. Both of these aspects of the invention include the catheter body defining at least one infusion lumen having an exit port located in the gap.
According to one aspect of the invention, the first balloon and second balloon wrap tightly around the distal region of the core without a gap between the first and second balloon.
According to another aspect of the invention, a sheath surrounds the first and second balloons to inhibit coagulate formation. The sheath is distanced from the first and second balloons according to a variation of the invention. The sheath contacts the first and second balloons according to an alternate variation of the invention.